Gender-bending chemicals: facts and fictionFears about the effects of endocrine-disrupting chemicals - commonly referred to as gender-benders - are rife. But where's the evidence that we have something to be scared of?

The supposed dangers posed by chemicals in household products make great headlines. But is there anything more to these dangers than that?

'Fertility threat to four out of 10 men', cried the front page of the UK Daily Mail on 28 June 2001 (1), headlining concerns about the continuing use, in everyday household products, like furniture and flooring, plastic goods, food packaging and cosmetics, of chemicals suspected of being able to mimic the action of human hormones. Another story, carried by the UK Sunday Telegraph, drew readers' attention to the 'Chemical peril hidden in homes' (2), pointing out that there is no requirement in law for members of the public to be told what chemicals may be contained in manufactured goods.

These are just two recent examples of the emotionally charged character of the debate surrounding so-called endocrine-disrupting chemicals (EDCs) - commonly referred to by the media as 'gender-benders', because of their potentially oestrogenic or anti-androgenic properties.

The articles in question drew upon a review published by Richard Sharpe of the Medical Research Council laboratories in Edinburgh, published in a recent issue of Toxicology Letters (3). This in turn relied upon two further studies that have suggested the possibility of EDCs affecting humans at doses lower than had previously been considered possible (4). But while Sharpe's paper presented the new evidence in a measured fashion, the translation of his points into the popular press has been sensational and one-sided. Why?

EDCs are the issue in toxicology today. Despite the fact that there is very little known as to their true extent, action or effect - or maybe because of this - many environmental campaigners argue that the use of all such substances, or even substances suspected of being such, should be banned altogether on precautionary grounds.

Yet one thing we do know categorically is that far more of these chemicals occur naturally in the food that we eat than they do in any artificial compound. In fact, there is a factor difference to the order of 40million (5). This is rarely reported by journalists, or even recognised by politicians and officials - who appear increasingly keen to devise policy based upon worst-case scenarios.

The experiments upon rodents used to measure the toxicity of particular chemicals lead to a determination of the so-called 'no observed adverse effect level' (NOAEL). This is based upon including ever-greater proportions of a substance into the diet of laboratory animals, until they develop any minor abnormality. The NOAEL itself is an extreme dose, unlikely ever to be encountered by any of us in our everyday use of products, even in combination. An additional margin of safety is usually added to this, typically a further factor of 100 - whether or not the effects noticed are plausibly transposable to humans.

The studies cited by Sharpe determined safety margins of 300 to 500. In other words, the subjects in question appeared to have been exposed to doses 300 to 500 times less than the equivalent dose that can produce marginal effects in rodents. As Sharpe uses an even more cautious safety factor of 1000, he considered the evidence to fall within this margin, and hence that it was worthy of note.

One could argue, therefore, that the story only exists because the safety goalposts have been moved by an additional factor of 10. Sharpe himself recognises that 'the data would still argue against' the possibility of causing adverse effects.

In the same issue of Toxicology Letters, an article by John Ashby of the Syngenta research Laboratory in Cheshire reminds us of the key effect of diet upon presumed endocrine-disrupting effects (6). He suggests that results suggesting low-dose effects of such chemicals from the laboratories of Frederick vom Saal in the USA, which have failed to be replicated, could be due to the overriding impact of the diet used upon the animals concerned.

Until there are clearly defined and commonly accepted protocols between experimenters across the world, then we are unlikely to uncover much hard fact in discussions about EDCs. No doubt it is levels of uncertainty within the whole debate that led Gail Charnley, a recent president of the USA-based Society for Risk Analysis, to describe the contemporary obsession with EDCs as deriving from 'a theory based on anecdotes', or 'a conclusion looking for data' (7).

And it is worth noting that the work of Richard Sharpe himself, which focuses primarily on the possibility of longitudinal reductions in human sperm counts, has previously been open to abuse by campaigners. In 1995, together with his collaborator Niels Skakkebaek, he felt compelled to publish a rebuttal in the UK Independent newspaper, in which he accused a high-profile campaigning environmental organisation of 'taking something which is a clearly stated hypothetical link and calling it a fact' (8).

A growing body of evidence now suggests that an exaggerated awareness of the possible risks associated with the use of chemical substances is itself driving an increase in psychogenic illnesses (9). For example, Sweden, the European country in the forefront of raising awareness and concern about these matters, suffers a notably higher incidence of somatic symptoms associated with the fears thereby raised than any other country in the developed world (10).

Real research into the properties of EDCs is not being helped through sensationalist reporting. A June 2000 Royal Society report indicated that 'it could be argued that some exposure to environmental, man-made chemicals with oestrogenic activity could be potentially beneficial rather than potentially harmful' (11). Yet when the first response to any discussion about EDCs is to push the panic button, how will we ever know?

Bill Durodiť is director of the International Centre for Security Analysis at King's College London. He is the author of Poisonous Dummies: European Risk Regulation after BSE, European Science and Environment Forum, 1999 (download this book (.pdf 679 KB)). He is also a contributor to Science: Can You Trust the Experts?, Hodder Murray, 2002 (buy this book from Amazon (UK) or Amazon (USA)); and Rethinking Risk and the Precautionary Principle, Butterworth-Heinemann, 2000 (buy this book from Amazon (UK) or Amazon (USA)).Read on:Household products - toxic shocks?, by Bill DurodiťLeap-frogging over science, by Bill Durodiť
(1) Daily Mail, 28 June 2001
(2) Sunday Telegraph, 1 July 2001
(3) Toxicology Letters 120 (2001), p221-232
(4) Blount et al and Colon et al, both in Environmental Health Perspectives 108
(5) SH Safe, 'Environmental and dietary oestrogens and human health: Is there a problem?', Environmental Health Perspectives 103 (1995) 346-351
(6) Toxicology Letters 120 (2001) 233-242
(7) SRA Risk Newsletter, Volume 19, Number 3, third quarter 1999
(8) Cited in 'Phthalate Plasticizers: Safely used in Vinyl Products for over 40 Years', Vinyl Council of Canada
(9) See, for example; 'Idiopathic environmental intolerances (IEI): myth and reality', H Staudenmayer, in Toxicology Letters 120 (2001) 333-342
(10) 'Psychological, social and media influences on the experience of somatic symptoms', S Wessely, paper presented to ESF workshop, Cognitive functions as mediators of environmental effects on health, 15 to 17 September 1997
(11) Endocrine-disrupting chemicals (EDCs) document, Royal Society, June 2000